Increased superoxide generation is associated with decreased superoxide dismutase activity and mRNA expression in placental trophoblast cells in pre-eclampsia

Pre-eclampsia is a multi-system disorder unique to human pregnancy. Althoug h the aetiology of pre-eclampsia is still unknown, increased placental oxid ative stress contributes to the pathophysiology of this pregnancy disorder. The goal of this study was to determine if placental trophoblast cells gen erate superoxide, and if there was a difference in superoxide generation an d superoxide dismutase (SOD) activity between trophoblast cells isolated fr om pre-eclamptic placentae versus normal placentae. Placentae were obtained from nine normal and 10 pre-eclamptic pregnancies immediately after delive ry. Trophoblast cells were isolated and purified by Percoll density gradien t centrifugation. Superoxide generation and SOD activity were determined by spectrophotometric assays. Localization of CuZn-SOD protein within the pla centa was examined by immunohistochemical staining. mRNA expression of CuZn -SOD was determined in trophoblast cells isolated from five normal and five pre-eclamptic pregnancies by Northern blot analysis. 18S ribosomal mRNA ex pression was used as an internal standard. We found (1) trophoblast cells f rom pre-eclamptic placentae generated significantly more superoxide than tr ophoblast cells from normal placentae: 17.62 +/- 3.19 versus 4.70 +/- 0.76 nmol/5 x 10(6) cells (mean +/- s.e.), P<0.01; (2) protein and mRNA expressi on for CuZn-SOD was mainly localized in the trophoblast cells within the pl acenta; and (3) SOD activity and relative mRNA expression for CuZn-SOD were significantly decreased in trophoblast cells from pre-eclamptic placentas as compared to trophoblast cells from normal placentae, SOD activity: 6.46 +/- 1.76 versus 13.01 +/- 1.67 units/mg protein, P<0.05; relative mRNA expr ession for CuZn-SOD: 0.25 +/- 0.09 versus 0.73 +/- 0.07, P<0.01. We conclud e that increased superoxide generation was associated with decreased SOD ac tivity and mRNA expression for CuZn-SOD in trophoblast cells isolated from pre-eclamptic placentae. These findings support the notion of increased oxi dative stress in the pre-eclamptic placenta, which may contribute to the pa thophysiology of this pregnancy disorder. (C) 2001 Harcourt Publishers Ltd.